This invention relates to a tool for use in applying lock wire to two or more threaded fasteners and specifically to such a tool which will tension the wire and then apply ferrules to the wire to hold it in place. In certain kinds of environments it is not sufficient simply to use nuts and bolts to hold parts together. In an airplane, for example, the loosening of a fastener could have disastrous consequences. Thus, it has been the practice for quite some time to use the type of fastener which has a hole extending transversely through the nut, the bolt head or the like and to pass a locking wire through two or more such fasteners. It has recently been proposed to apply ferrules to the ends of each wire passing through a set of fasteners.